Traditional RF electron accelerators are bulky. The transverse size of the RF electron accelerator is about four orders of magnitude larger than that of the optical electron accelerator. Traditional RF electron accelerators are also limited by smaller accelerator gradient (˜30 MV/m), compared to the optical electron accelerators (>1 GV/m). As a result, the accelerator length of the traditional RF electron accelerator is about one order longer than that of the optical electron accelerator. These physical limitations increase the difficulty of shrinking RF electron accelerators to tabletop sizes for portable applications.
Some optical electron accelerators use guided wave structures, which require accurate phase velocity matching between the laser pulses and the electron beams because the accelerating laser pulses are co-propagating with the electron beams. This increases difficulties in structure design (to match the phase velocity), coupler design (to couple light into structure efficiently) and integration between accelerators and other components.
As example of the current state of the art, a dielectric laser accelerator is described in U.S. Pat. No. 7,994,472 to Tomas Plettner and Robert L. Byer, “Laser-driven deflection arrangements and methods involving charged particle beams”, issued 9 Aug., 2011, which is incorporated herein by reference.